In a hydraulic excavator as a construction machine according to the prior art, a hydraulic pump for the supply of pressure oil to a hydraulic drive system such as a working attachment is driven by an engine, and a radiator is used for cooling the engine. The radiator is cooled by a cooling fan disposed downstream of and in proximity to the radiator. Heat radiating devices, including the hydraulic pump, other than the engine are air-cooled by contact therewith of cooling air which has been used to cool the radiator. As to the working fluid, it is cooled by an oil cooler disposed in series with the radiator.
Cooling air for cooling heat exchangers such as the radiator and the oil cooler both referred to above is usually introduced through an intake opening portion formed in a side face of an engine guard and exhaust air after heat exchange is discharged to the exterior through an exhaust opening portion formed in an upper surface of the engine guard.
In such a cooling structure, the intake opening portion is usually disposed in opposition to the heat exchanger, so that engine noise including noise of the cooling fan leaks directly from the intake opening portion to the exterior, causing noise in the exterior.
With a view to diminishing the leakage of engine noise to the exterior there has been proposed a soundproof device wherein a splitter sound deadening device is disposed in close contact with a radiator opening portion [see, for example, pages (3) and (4), FIGS. 4 and 6, of Japanese Patent Laid-Open Publication No. Hei 6-144022 (Patent Document 1)].
In the splitter sound deadening device, a duct-shaped box member is attached to a passage of exhaust air which is discharged from a radiator by an extrusion cooling fan and then discharged from an exhaust opening portion of an engine guard, the interior of the box member is partitioned to a plurality of exhaust air chambers, and a sound absorbing material is affixed to the inner wall of each exhaust air chamber to reduce noise.
On the other hand, as an arrangement wherein an intake opening portion and a radiator are not opposed to each other, there has been proposed an arrangement wherein a duct connected between an intake opening portion and a radiator is bent in to an L shape and the intake opening portion is disposed toward the center of the machine body [see, for example, page (2), FIG. 1, of Japanese Patent Laid-Open Publication No. Hei 8-218869 (Patent Document 2)].